Color liquid crystal display projectors generate display images and project them onto display screens, typically for viewing by multiple persons or viewers. The display images may be formed by transmitting light from a high-intensity source of polychromatic or white light through an image-forming medium such as a liquid crystal display (LCD).
In projection display applications, light brightness is an important performance feature. U.S. Pat. No. 5,161,042 of Hamada describes a color liquid crystal display projection system that utilizes a sequence of red, green, and blue inclined dichroic color selective mirrors to form angularly color separated color component light beams without the brightness losses caused by conventional color filter mosaics. The separate color component light beams are directed to an array of microlenses each of which converges the light beams onto one picture element aperture of the liquid crystal display.
A disadvantage of such a system is that the angularly color separated color component light beams would typically be implemented with relatively large color separation angles of, for example, 6 degrees per color component channel. While providing relatively efficient color-separated illumination, such large color separation angles can require that the projector projection lens arrangement have a low F-number of f2.5 or less. F-number is a ratio of the pupil or aperture size (e.g., along a horizontal direction) to the focal length of the lens arrangement. Projection lens arrangements with such low F-numbers can be difficult to manufacture and are susceptible to various optical aberrations that can degrade the display image quality.
Accordingly, one implementation of the present invention includes a color liquid crystal display projector having a light source with a radiating element (e.g., arc or incandescent) and a liquid crystal display (LCD). The LCD includes an array of multiple picture elements or pixels that each have separate color component sub-pixels (e.g., red, green and blue). Multiple differently inclined dichroic mirrors angularly separate the light into light beams of different color components. An integrating lens array relay system has a pair of planar lens arrays that form multiple spatially separated images of the angularly-color separated light components. A microlens array positioned adjacent to the LCD images the spatially separated images upon the color component sub-pixels of the LCD.
More specifically, the first planar lens array receives white light and forms in the second lens array color component (i.e., red, green, and blue) images of the light source (i.e., the radiating element). Color component filters may optionally be positioned adjacent the second lens array to filter these color component images, rather than filtering them at the LCD as is conventional and more expensive to implement. The color component light source images formed in the second planar lens array match and are mapped to the color component sub-pixels of the LCD. Each microlens in the microlens array directs light from the multiple spatially separated images into corresponding sub-pixels of multiple ones of the pixels.
Additional objects and advantages of the present invention will be apparent from the detailed description of the preferred embodiment thereof, which proceeds with reference to the accompanying drawings.